Expression And Its Significance Of The AQP4 After Brain Injury Model In Rats

Objective: To investigate the changes of aquaporin-4(AQP4) expression after traumatic brain injury in rats,and its correlation with the cerebral edema.Methods: Two hundreds Healthy Wistar rats (W=200~250g) were randomly divided into 2 groups, the control group and the traumatic brain injury(TBI) group. And then the rats were subdivided into 5 groups(five rats for each) at an interval of 1h, 2h, 3h, 24h and 72h respectively. The TBI model was established by improved Feeney method. The brain water content(BWC) was measured by dry-wet Weight methods. The pathological changes of the injury brain tissue were observed under light microscope(LM) and transmission electron microscope (TEM). Immunohistochemistry (IHC) method was used to detect the changes of the AQP4 expression. The results were analyzed by means of Computer-aided Image Analyzer.Results: The expression of AQP4 was mainly located in the choroid epithelial cells and ependyma in the control group. The expression of AQP4 significantly increased at 1h after brain injury. The AQP4 positive cell were observed in the choroid plexus, ependyma, hippocampus, dentate gyrus, supraoptic nucleus, paraventricular nucleus, cerebral cortex, and scattered in dorsal thalamus, basal nuclei, granualar layer of bilateral cerebral cortexes alongside the cerebral longitudinal fissure. The expressin of AQP4 had its peak at 3h. Then, the expression of AQP4 decreased with the duration of time. The AQP4 positive cells were located around the traumatic region, choroid plexus and sub-cerebral cortex at 24h and 72h. Except 24h and 72h, the optical density(OD) was significantly different at 1h, 2h and 3h compared with the control group(p<0.05). The BWC of injured side was slightly increased at 1h, 2h and 24h. At 72h the BWC was significantly increased(P<0.05).TEM showed only at 3h after brain injury the mitochondrion edema was observed in neurons; at 24h the obvious mitochondrion edema appeared, the structures of organellae were unclear with the nucleus dissolved; at 72h the mitochondrion edema was still observed.Conclutions:1. At the earlier period of the TBI, the expression of AQP4 was strongly incresed. It regulated the balance of water and electrolyte in CNS and maintained the normal function of the CNS. At the same time , the brain edema was gradually improved. The results imply that the AQP4 may participate the stress reaction at earlier stage of the TBI .2. At the later period of a TBI, the expression of AQP4 was down-regulated . However, the BWC was increased. The results suggested the change of AQP4 activity and other factors might result in the formation of brain edema in the later stage of TBI.